1. Field of the Invention
The present invention is directed to a dual cartridge seal, and in particular to a cartridge dual seal structure, and a method for operating a cartridge dual seal, wherein barrier fluid flow is optimized in order to promote cool running of the seal.
2. Description of the Prior Art
A cartridge dual seal is used in a journal or bearing for a rotating element, such as a rotating shaft, in order to permit rotation of the shaft relative to a stationary element, while maintaining a seal for lubricant or in seals for pump shafts for sealing process material from the environment. Such a mechanical seal assembly typically includes one or two pairs of seal rings, one seal ring in each pair being stationary with respect to the seal assembly housing, and the other seal ring in each pair being mounted for rotation with the shaft. The seal rings in each pair respectively have faces in sliding contact with each other. When two such pairs of seal rings are used, a volume between the seal rings may be flushed with a barrier fluid in order to cool and lubricate the seal, as well as to provide a secondary source of sealing and/or a source of lubrication.
The basic structure of a known cartridge dual seal is shown in FIGS. 7 and 8.
FIG. 7 shows the basic components, and FIG. 8 shows the same components plus further structural details. A seal assembly 2 is mounted on a rotatable shaft 1. The seal assembly 2 includes a sleeve 3 fitted around the shaft 1 and held in place, together with other components by a locking ring 4. Between the sleeve 3 and the locking ring 4, two rotating seal rings 5 and 6 are held in place, with the assistance of gaskets (e.g., O-rings) 12 and 13. The rotating seal ring 5 has a face which is in sliding contact with a face of a stationary seal ring 7, and the rotating seal ring 6 has a face which is in sliding contact with a face of another stationary seal ring 8. The seal rings 5 and 7 form a first seal ring pair, and the seal rings 6 and 8 form a second seal ring pair.
The stationary seal rings 7 and 8 are held in place between the rotating seal rings 5 and 6 by a spacer 9, disposed between the stationary seal rings 7 and 8. The spacer 9 has an opening therein, described in more detail in connection with FIG. 8, through which barrier fluid is introduced into a barrier fluid chamber 10, as viewed in a radial plane completely containing the shaft axis. The sleeve 3 has an outer surface 3a, and the barrier fluid chamber 10 is defined by the continuous spaces between the surface 3a and the spacer 9, between a surface 7a of the stationary sealing ring 7 and the surface 3a, between a surface 8a of the stationary sealing ring 8 and the surface 3a, and axially-spaced edge volumes respectively between the rotating sealing ring 5 and the stationary sealing ring 7, and between the rotating sealing ring 6 and the stationary sealing ring 8. As is conventional, and as shown in FIGS. 7 and 8, the surfaces 7a and 8a are coplanar and parallel to the surface 3a.
Further structural details of the sealing assembly 2 can be seen in FIG. 8. The locking ring 4, and the components contained therein, are held in place on the rotating shaft 1 by means of clips 15 each having a peg which respectively extends through corresponding openings in the sleeve 3 so as to abut the outer surface of the shaft 1. One such peg 16 extending through one such opening 17 can be seen in FIG. 8. The lock ring 4 is tightened onto the shaft 1 by a number of set screws (not shown). A screw 18 attaches the clip 15 to the lock ring 4.
As also shown in FIG. 8, the rotating sealing ring 5 is urged into sliding contact with the stationary sealing ring 7 by means of a spring 20. A pin 19 engages the lock ring 4, thus imparting rotation to the rotating sealing ring 5. The spring 20 is a compression spring, and thus forces the rotating sealing ring 5 against the stationary sealing ring 7. An identical arrangement is used for the rotating sealing ring 6, but in view of the other components in the vicinity, reference numerals and lead lines have been omitted to improve the clarity of the drawing.
As also shown in FIG. 8, a housing 21 via which barrier fluid is fed from a barrier fluid source by a pump or other pressure source 28 into the barrier fluid chamber 10 is disposed above the stationary sealing rings 7 and 8, with O-rings 26 and 27 being disposed between the housing 21 and the respective stationary sealing rings 7 and 8. The housing 21 contains an opening 22, which may be threaded, in order to receive a conduit or other means for introducing barrier fluid from the barrier fluid source via the pressure source 28. The opening 22 communicates with the chamber 10 via a barrier fluid inlet 23. The barrier fluid exits the chamber 10 (minimally) through the respective interfaces between the sealing rings 5 and 7 and the sealing rings 6 and 8.
The housing 21 has an annular channel 24 which is in engagement with a lip 25 of the clip 15, so as to fix the relative positions of all of the components during installation. Additional O-rings 11 and 14 are provided as needed.
As noted above, one of the purposes of the barrier fluid introduced to the barrier chamber 10 is to lubricate and cool the seal assembly 2, particularly the confronting faces of the sealing rings 5-8. For this purpose, it is important that the barrier fluid not be stagnant in the chamber 10, otherwise heat pockets having unacceptably high temperatures develop in the chamber. For this purpose, the barrier fluid can be circulated through an external cooling system to remove heat from the seal and to maintain sufficiently low face temperatures. The success of these known systems, however, depends largely on the ability of the barrier fluid to reach the warmest regions of the seal, namely the respective interfaces of the sealing ring pairs. This has been a persistent problem in the art because the interfaces are located at the end or edge regions of the barrier fluid chamber, whereas the barrier fluid is introduced in a central region of the chamber. The barrier fluid chamber, because of confinements necessitated by the overall seal structure, offers flow passages between its central region and its edge regions which are relatively narrow. Efforts to improve the flow behavior of the barrier fluid in the barrier fluid chamber, and thereby to promote more efficient heat removal, have included the use of conventional flow enhancing components, such as baffles (which require large amounts of space), but the problem of efficient heat removal from the interfaces in a cartridge dual seal still has not been satisfactorily resolved.